Soil Stabilization Firm Grouting Largest US Sinkhole
In one of the largest sinkhole grouting projects undertaken in the United States, Earth Tech, a soil stabilization firm located in Land O’ Lakes, Fl is using concrete pumps to provide a firm foundation for a ramp improvement on Interstate-4 (I-4) at Maitland Boulevard in Orlando. More than 35,000 yards of grout will be pumped on the project which is one-third of the way through a nine month schedule of completion.
“Sinkholes form in central Florida because the soil and geology in the area is a deep layer of limestone with a sandy overlay,” explains Ron Broderick, Earth Tech president, “Think of an hourglass and slowly seeping sand and that is a simple description of the soil overlay penetrating the limestone causing a sinkhole.” There are two types of sinkholes: subsidence sinkholes that develop gradually like the I-4 situation; and collapse sinkholes. This second type can be catastrophic as when a sudden collapse of the subsoil in Winter park FL swallowed an entire house, numerous trees, half of a six-lane highway, half of a public swimming pool, and parts of three businesses all in 24 hours. The sinkhole created by that disaster was 300-feet by 320-feet. The I-4/ Maitland Blvd. sinkhole is approximately 325-feet in diameter.
Earth Tech began in 1991 and built on Ron and father Lewis’ experience with a large drilling and grouting contractor in Pennsylvania. The Broadrick’s recognized the unique market Florida offered where commercial and residential sites often require soil stabilization to be buildable. There are more insurance claims for soil failure in some counties of Florida than there are for fire damage. In order to meet the growing demand for soil stabilization, Earth Tech now employs more than 100 people. They are reactive when soil conditions threaten existing structures and preventative as in the I-4 situation where FDOT is anticipating highway improvements.
The method to stabilize the I-4 requires drilling and pumping grout at prescribed intervals to stabilize the area for the long term. Earth Tech’s crew of 12 is following an engineering plan developed through ground radar and penetration of the soil layer to measure the relative density of the soil. The area was dewatered and demucked prior to drilling. Then the entire area was filled with sand and compacted to provide a base for the Earth tech drill rigs.
More than 300 injection points were recommended by the engineer on the project. After drilling and installing a casing at every injection point, Earth Tech relies on two of their 10 Schwing SP 1000s to pump grout as deep as 350-feet. The company has erected one of their batch plants on-site to discharge directly into the pump hoppers for continuous grouting. “With the job requirements on this project we did not want to depend on material deliveries,” explained Broderick.
The sequence of filling the sinkhole requires the drill rig to penetrate to the limestone. Then the pump places approximately 50 yards of the 5-inch slump material through three-inch hose. This raises the level of the cap approximately two-feet at each injection point. Pumping pressures of up to 350-psi are achieved as the grout displaces soils and builds up in the void. The SP 1000s perform simultaneously and effortlessly pumping to separate injection points with their 70 cubic yard per hour capacity, 133 horsepower diesel engines and ability to apply up to 1100 psi on the material. The company expects to continue with this method for nearly nine months averaging 500-750 cubic yards of pumped grout per day at 10-12 injection points.
“We train our own crews and assign them specific tasks. On this job we have specialists on the volumetric batch plant, on the hydraulic drill rigs and on the pumps,” according to Broadrick, “We have used Schwings for the last 16 years because we respect their reliability.” He added that, “The Schwing Rock Valve does not allow water leakage like conventional swing tubes which with our slow delivery volumes and high pressures can cause a “sand block” within the pump mechanism. We don’t have that problem with our Schwing pumps. The Rock Valve also reduces water for clean-up and provides easy change-out of wear parts.”
Earth Tech’s commitment to proper soil stabilization and to their marketplace is evident in Broadrick’s efforts to protect the industry. He and other reputable contractors in Florida formed The Florida Association of Sinkhole Stabilization Specialists to develop standards, track legislation and educate the public. “It has developed over the passed several years so that if a contractor is not a member, there’s probably a reason,” explains Broadrick, “Many subsurface problems can create emergency conditions and we want the public and government to have experienced contractors who can mobilize fast and proceed quickly with the correct remediation.”
Project: I-4/Maitland Boulevard Sinkhole Stabilization, Orlando, FL
Owner: Florida Department of Transportation
Concrete Pumping Contractor: Earth Tech, Land O’Lakes, Florida
Equipment: Two Schwing SP 1000 stationary concrete pumps